The present invention relates to high basicity polyaluminumchlorosulfates and their preparation process, and to the application of such polyaluminumchlorosulfates to the treatment of drinking water, aqueous effluents, and in the papermaking industry.
Polyaluminumchlorosulfates are widely used in industry, notably the papermaking industry and in the treatment of their waste water and water intended for drinking, because of elevated coagulating and floculating ability. The performance and applications of these polyaluminumchlorosulfates is of course a function of their main characteristics. For the treatment of water intended for drinking, high basicity is required; for effective floculation, a high sulfate content is required; and for all applications, the compounds need to be stable.
Polyaluminumchlorosulfates the formula of which is Al.sub.n OH.sub.m (SO.sub.4).sub.k Cl.sub.3n-m-2k have a relatively high basicity, which can reach 65%. These products, described in FR-A-2 584 699, nevertheless suffer from the major disadvantage of leading to the production of gypsum as a by-product during their manufacture, the discharge of which presents environmental problems.
JP-52 113,384 describes and claims a process for producing high basicity polyaluminumchlorosulfates by adding, at a temperature less than 60.degree. C., an alkaline agent such as CaCO.sub.3, NaHCO.sub.3, Na.sub.2 CO.sub.3, Mg(OH).sub.2 or MgO to a solution of a polyaluminum compound previously obtained by reacting a low basicity polyaluminumchlorosulfate with CaCO.sub.3, leading to the production of gypsum which is separated out, the basicity of this intermediate polyaluminum compound being 50.
JP-53 001,699 describes and claims a process for producing high basicity polyaluminumchlorosulfate in which, in a first stage, a medium basicity polyaluminumchlorosulfate is reacted with an equimolar, based on the sulfate, amount of CaCO.sub.3, leading to the production of gypsum which is separated out, after which, in a second stage, the product from the preceding stage having a basicity comprised between 55 and 58, is reacted with a compound selected from the group comprising: CaCO.sub.3, NaHCO.sub.3, Na.sub.2 CO.sub.3, Mg(OH).sub.2 and MgO.
Nevertheless, the basicity of the polyaluminumchiorosulfates according to these two Japanese documents above is less than 70% and hence, in certain applications, is not sufficiently high. Moreover, these compounds have poor stability. One major disadvantage that these compounds suffer from is the production of gypsum the discharge of which presents an environmental problem, as mentioned previously.
FR-A-2 317,227 describes and claims a process for producing, at a temperature less than 50.degree. C., aluminum hydroxychlorides of general formula: EQU Al(OH).sub.a Cl.sub.b Y.sub.c/z1 M.sub.d/z2
in which:
Y is an anion of valency z1, typically SO.sub.4.sup.2- ; PA1 M is a cation of valency z2, such as ammonium, an alkaline or alkaline-earth metal; and PA1 1.2&lt;a&lt;1.7; PA1 0&lt;c.ltoreq.0.6; PA1 0.2&lt;d&lt;1.7; and PA1 a+b+c=3+d. PA1 M is an alkaline-earth metal; PA1 N is an alkaline metal; PA1 a, b, c, d and e are numbers such that: PA1 2.05&lt;a&lt;2.25; 0.04&lt;c&lt;0.06; PA1 0.1&lt;d&lt;0.13; 0.4&lt;e&lt;0.8. PA1 M is an alkaline-earth metal; PA1 N is an alkaline metal; PA1 a, b, c, d and e are numbers such that: PA1 1&lt;a'&lt;1.95; 0&lt;c'&lt;0.15; PA1 a'+b'+2c'=3; PA1 1.1&lt;a'&lt;1.4; 0.04&lt;c'&lt;0.06; and PA1 0.1&lt;M/Al&lt;0.13 and 0.4&lt;N/Al&lt;0.8.
However, in this patent it is stated that even though the use of alkaline-earth metals is possible, the danger of precipitates appearing does exist, leading to poor stability.